In recent years, with the improvement in the degree of integration of ULSIs that form the core of microelectronics, circuit patterns in these quantum devices have been increasingly miniaturized. Conventionally, in fabrication processes of semiconductor devices, as basic techniques for removing unnecessary parts of insulating layers and thin metal layers with a high degree of accuracy along resist patterns, various etching methods have been widely employed. As one of these etching methods, dry etching using a halogen gas can be mentioned. This dry etching has been anticipated as being capable of fabricating a structure such as a minute quantum device since etching is carried out in a relatively clean atmosphere in a high vacuum.
For example, for Si, which is a representative device material, a dry etching process by a fluorine and chlorine-based halogen gas has been carried out. In addition, there are many reports on a dry etching process with regard to compound semiconductors such as AlxGayIn1-x-yAszP1-z including GaAs as well, however, as a matter of fact, a technical means for enabling fabrication of a quantum element has not been completed.
For example, GaAs is a material that is great in mobility compared to Si and is capable of a higher-frequency and higher-speed operation than that of Si, and in place of Si, which has developed on an industrial scale based on advantages such as abundance in resources and crystal integrity, this has been attracting attention for its excellent properties and diversity as one of the component semiconductors to overcome limitations thereof. Moreover, as epitaxial crystal growth techniques for compound semiconductors such as this GaAs, techniques such as an MBE (molecular beam epitaxial growth) method and an MOCVD (metal-organic chemical vapor deposition) method have advanced to allow a high-quality crystal growth, therefore, importance of compound semiconductors as device materials has been increasing.
Therefore, as a dry etching method for overcoming technical limitations of a conventional dry etching method using a halogen gas for a compound semiconductor or the like, the present inventor has developed a method for dry-etching the surface of a semiconductor crystal by a bromide in single atomic layer units and has disclosed the same in Japanese Published Unexamined Patent Application No. H08-321483.
However, in order to form a circuit pattern on the surface of a GaAs layer with accuracy, it has been necessary to form a dry etching mask even when dry etching is carried out in single atomic layer units as described above.
Conventionally, fabrication of this dry etching mask has been carried out by use of an electron beam lithography technique as described in Japanese Published Unexamined Patent Application No. 2001-267213, for example.
However, with miniaturization and a greater complexity of circuit patterns of quantum devices in recent years, it has become difficult to fabricate this dry etching mask itself, therefore, a problem has existed in that reproducibility of shape and size has deteriorated, and furthermore, cost considerably has risen.
Moreover, since a surface oxide layer such as As2O3, As2O, or Ga2O has been naturally formed on the surface of a GaAs layer, when forming a dry etching mask, it has also been necessary to remove this surface oxide layer.
The present invention has been made in view of the problems, and an object thereof is to provide an electron beam micro/nano fabrication method for forming on the spot, on the surface of an AlxGayIn1-x-yAszP1-z including GaAs, a minute circuit pattern having different aspect ratios used for a quantum device without necessity for removing in advance a surface oxide layer such as As2O3, As2O, or Ga2O naturally formed on the surface of a GaAs layer and also without forming a dry etching mask for forming a miniaturized complex circuit pattern.